1. Field of the Invention
The invention relates to an apparatus for effecting group management of elevators which is responsive to a floor call for selecting an appropriate elevator from among a plurality of elevators and assigning it to the floor call, and to a method of effecting such group management.
2. Description of the Related Art
In general, a group management service is conducted in a building structure provided with a plurality of elevators. An assignment system is a typical example for effecting the group management service. The assignment system is arranged to calculate an assignment value for each car promptly after a floor call has been registered, select a car having an optimum assignment value, and assign the car to the floor call for the purpose of service. In the assignment system, since only a specified car is allowed to respond to the floor call, it is possible to realize an improved service efficiency and a reduced waiting time. In such an assignment type of group management elevator, it is common practice to dispose arrival warning lamps associated with each car and each direction of car travel at each terminal floor. Persons waiting at each terminal floor are informed which car has been assigned to the floor call by means of a warning indication provided by the arrival warning lamps. Accordingly, the waiting persons can easily move to the front of the door of a hatchway in which the specified car is located.
In the above-described floor-call assignment system, assignment values are calculated to determine which car should be assigned to a floor call of interest on the assumption that the current situation will change proportionally. More specifically, the predicted value of the time required for each car to arrive at each terminal floor in response to the floor call in sequence (hereinafter referred to as a "predicted arrival time") and the time elapsed after the floor call has been registered (hereinafter referred to as an "elapsed time") are obtained on the basis of the current position and direction of each car as well as the currently registered floor calls or car calls. In addition, predicted waiting times for all the currently registered floor calls are calculated by adding the predicted arrival time and the elapsed time. The sum of the predicted waiting times or the sum of the squares of the predicted waiting times is obtained and set as the aforesaid assignment value, and a car having a minimum assignment value is in turn assigned to the aforesaid floor call. However, such a conventional system has a number of problems. For instance, a decision as to whether the assignment of the floor call is optimum must be made on the basis of the current situation. As a result, if a user newly registers a floor call after the aforesaid assignment has been completed, the conventional system compels the user to wait for an excessively long time.
The aforementioned problem will be explained in further detail with reference to the example shown in FIGS. 15-18. Referring to FIG. 15, a first car A is travelling upward in response to a car call 6c of the sixth floor, while a second car B is assigned to an upward call 5u of the fifth floor and is travelling in response to an upward assignment 5uB. In this state, a downward call 9d is registered at the ninth floor as shown in FIG. 16. If an assignment value is obtained in accordance with the above-described conventional assignment system, the ninth-floor downward call 9d is assigned to the car A so as to minimize waiting time on average. The car A is given a downward assignment 9dA of the ninth floor, with the result that the two cars travel upwardly.
If an upward call 1u is registered at a lower floor, for example, at the first floor, a time delay after the downward call 9d of the ninth floor has been registered, the upward call 1u of the first floor is the second call with respect to the cars A and B. Even if the upward call 1u is assigned to either car, it will take a long time for the assigned car to respond thereto and users are compelled to wait for a long time.
If the downward call 9d of the ninth floor is assigned to the car B, it is expected that, as shown in FIG. 17, about 15 seconds thereafter, the car A stops as an empty car at the sixth floor, while the car B is in service at the fifth floor, where a car call 10c of the tenth floor is assumed to be registered. In this case, even if the upward call 1u of the first floor is registered thereafter, the car A waiting at the sixth floor promptly moves to the first floor as shown in FIG. 18. Accordingly, users are not compelled to wait for a long time. As described above, to prevent the occurrence of a long waiting time, how the cars will be located in the near future and the possibility of a particular car becoming empty are considered and it is necessary to assign each floor call so as not to gather many cars at a specific location, although the assignment may temporarily lead to a long waiting time.
As will be explained below, a variety of proposals have been made with respect to a method capable of assigning floor calls so as to prevent many cars from gathering at a single location. However, with all of the proposed methods, the problem of excessive waiting times is present.
Japanese Patent Publication No. 55-32625 discloses a group management apparatus for elevators in order to prevent all cars from gather at a single location and improve service efficiency. The disclosed apparatus utilizes an assignment system in which, when a floor call is registered, this floor call is assigned to a car which is expected to stop at a terminal floor near the location where the floor call has occurred. However, such a conventional assignment system still involves the problem of long waiting time. This is because the conventional system merely pays attention to the presence or absence of a car which can stop at a nearby floor and makes no appropriate decision as to how long it takes until the car arrives at the floor of interest, how other registered floors are distributed, when a response to each of the other registered floors is provided, whether there is a car which will become empty in the near future, at what floor each car other than the car of interest is located, in what direction each car is about to travel, and so on.
Japanese Patent Publication No. 62-56076 discloses a group management method for elevators. The disclosed method is characterized by an assignment method in which a car is placed in a stand-by state at a floor where the last passenger has got off. The assignment method comprises the steps of: temporarily assigning a new floor call to each car in sequence to predict the locations where the respective temporarily assigned cars are rested; calculating the degrees of dispersion of the cars from the predicted stand-by locations of the respective temporarily assigned cars and the locations of the other cars; and setting at least the aforesaid degrees of dispersion as evaluated values for the respective temporarily assigned cars in such a manner that a car having a larger degree of dispersion is more easy to assign to the floor call, thereby selecting a specific car to which the floor call should be assigned on the basis of the evaluated values of the respective cars. In the assignment method having the above-described arrangement, even after the service of the floor call has been completed, the cars can be widely dispersed to prevent unnecessary empty cars from being moved in their dispersed stand-by states. Accordingly, the above-described assignment method has the advantages that considerable energy savings can be improved and that residents in a building can use elevators without nuisance. However, as is evident from the object disclosed in Japanese Patent Publication No. 62-56076, the above assignment method is intended for infrequent services, as in the nighttime and is based on the assumption that a single floor call is registered when all the cars are empty and at rest. For this reason, this assignment method cannot be applied to the assignment of floor calls under the service condition of floor calls being registered one after another with cars travelling in response to many calls, thus resulting in the problem of a long waiting time. A first reason why this problem results is that the above-described assignment method is intended to balance the positions of empty cars and therefore, is not arranged to allow for variations with time in the positions of the respective cars other than the aforesaid temporarily assigned cars. As can be seen from the assumption of such an assignment method, it is not necessary to allow for variations in the positions of the other cars. A second reason is that a decision as to the assignment of floor calls is made by paying attention to only the position which is taken by the aforesaid temporarily assigned car when the last passenger gets off and this car comes to a rest. (At this time, all the cars are empty and at rest.)
Another new group management system utilizing a fuzzy theory is proposed in "GROUP MANAGEMENT APPARATUS FOR ELEVATORS", a collection of papers, Vol 2, P 2, 117-120 published in a 1988 meeting associated with electricity and information technologies, held at the department of engineering of Niigata University on October 3-5, 1988. This paper described the following example. When a floor call occurs at, for example, an upper floor, if it is likely that, when this floor call is assigned to a certain car A, cars will gather at the upper floor, car candidates for assignment are specified except for a car or cars having this likelihood, and a car having a minimum assignment value is selected from among these car candidates for assignment.
This paper describes a certain simulation example such as that shown in FIG. 19. In the illustrated state, if a downward call at the tenth floor is registered, it is preferable that the car having the better assignment value be selected as an assigned car from a first car and a third car, each having a car call of an upper floor, not a second car and a fourth car which are empty. According to the teaching, it is possible to realize an assignment scheme in which a floor call which will occur in the near future is taken into account, whereby the occurrence of a long waiting time can be prevented. However, in this simulation example, the decision as to whether the cars gather at the upper floor is made on only the condition of "having a floor call at an upper floor" or "having an assigned call at an upper floor", and a variation in the positional relationship between the cars with time is not taken into account. Any car may arrive at the upper floor, but, since positional relationship with the other cars is not clearly determined, it is highly probable that cars will not "gather at the upper floor". In this case, waiting time will become even longer just because the empty cars are eliminated from the assignment.
The above-described problem will be explained in further detail with reference to the example shown in FIGS. 20-22. Referring to FIG. 20, the first car A is travelling upward through the fourth floor in response to the car call 6c of the sixth floor, while the second car B does not have a call of the sixth floor and is empty with its door closed. In this state, the downward call 9d is assumed to be registered at the ninth floor as shown in FIG. 21. According to the fuzzy rules described above, if the downward call 9d of the ninth floor is assigned to the car B, it is determined that the cars A and B gather at an upper floor. Accordingly, a car other than the empty car B--the car A in this example--is set as a car candidate for assignment, and the downward call 9d of the ninth floor is assigned to the car A. Accordingly, if the upward call 1u is registered at a lower floor, for example, the first floor, immediately after the downward call 9d of the ninth floor has been assigned, the upward call 1u of the first floor is assigned to the car B which is rested at the sixth floor and the car B promptly travels to the first floor. Therefore, an excessively long waiting time does not occur.
However, as described above, it is effective to exclude empty cars in only a service condition in which a floor call tends to relatively frequently occur at a lower floor. In the case of a considerably intermittent service condition in which no floor call appears at the lower floor for a while, the following arrangement is advantageous in minimize waiting time on average. The empty car B is caused to respond to the downward call 9d of the ninth floor. Then, regarding a floor call which will occur after a while, the car A which is expected to be empty at that time is caused to respond to the floor call; for example, if the downward call 9d of the ninth floor is not assigned to the car A, the car A, as shown in FIG. 22, completes its service at the sixth floor and becomes empty 15 seconds later.
As described above, in the conventional method, empty cars are eliminated from assignment processes without allowing for the probability that a car (or predicted empty car), which completes responding to a floor call and comes to a rest with its door closed, will appear in the near future. Accordingly, the problem of an insufficient reduction in waiting time still arises.